containing particles of living matter which have most importtant functions in health, while similar particles in a diseased state may act as noxious living stimuli on the healthy plastids of distant parts, and thus convey specific diseases. This idea has recently received an important application in the theory of secondary cancer put forth by Dr. Creighton, and received with favour in the medical world. * The theory is that the secondary cancerous tumor is not caused by the transplantation of complete cancerous cells from the primary tumor, which take root in a different organ and grow there, but that it is produced by the transformation of the previously healthy cells of the organ-say the liver-by the operation of an extraneous influence, "which is to be compared to a spermatic influence produced in some unknown manner by the parent tumor." Thus the quasi-sexual operation of partial bions, or portions of living matter thrown off by healthy or diseased living tissues and organs, may have an extensive application within the body itself, and it is only natural to extend the same principle to the action of one body on another in explanation of the nature of contagious diseases.

I conclude, therefore, that an assumption of a conjugational or quasi-sexual power in the partial bions constituting the exciting cause of the specific infectious diseases would remove the objections applying to both the parasitic and the simple graft-germ theories, which tell especially in the fevers of the smallpox group. I propose, therefore, to add the term conjugation-germ to those already in use. (§ 17.)

To go into the detailed application of these principles to the infectious diseases in general is impossible, as my space is nearly exhausted. A few words only on their applicability to the clinical facts of the smallpox group, which demand that the multiplication of the poison shall depend on the co-operation of the organism, and not on the self-multiplica* Privy Council Health Reports, 1874.

tion of a foreign organism merely sojourning within it. At the time of infection of smallpox we may imagine the conjugation-germs absorbed and diffused in extremely minute subdivision through the whole blood, whence they are speedily removed and blended with the fixed plastids specifically adapted to combine with them, for the blood, as a rule, does not convey the disease. In the latent stage, some unknown change, in addition to that which happens with all stimuli, is taking place, like the early stage of conception, which gives rise to few symptoms. Some, however, can be detected; for instance, wounds will not heal at that time. At the period of invasion the sudden and enormous reproduction of the specific partial bions from the infected fixed plastids begins, thus causing the initiatory fever. But the reproduction of the specific partial bions is not the proximate cause of the whole febrile symptoms; for the irritation of that process causes a large amount of the febrile disturbances which are common to all kinds of fever, including those arising from non-specific causes. We have the irregular distribution of blood from irritation of the vaso-motor centres (which though attracting most attention is less important), and, above all, the increase of the bioplasts of the blood and capillaries, which is the essential proximate cause of the febrile and inflammatory states. This is recognised by Dr. Beale, who points out that not all the abundant masses of germinal matter and bioplasts found in infective ophthalmia are the descendents of the infecting graft-germs, but many or most are simply the superabundant formation of non-specific bioplasts, which is the essence of inflammation and fever. This is important, as the non-specific part of the disease greatly complicates and aggravates the total result, and may be what determines the fatal event in particular cases. Besides therefore the varying susceptibility to the specific poison, we have the same variety

towards common exciting causes, for no two people suffer alike in degree from the common causes of disease, such as cold or other perversions of the ordinary conditions of health. Hence a double cause exists for the varying intensity of the total disease in different persons; and hence also the existence of a margin of possible success in treatment, even although we may not possess a specific antidote for the specific poison. Another subordinate complication of some specific diseases is the presence of saprophytic parasites, which may contribute largely to the severity of the total disease. Their relation to the specific cause has been already dealt with. (§ § 10, 11, 12, 13.) In some specific diseases we are probably concerned only with graft-germs propagating asexually; in others, especially those both inoculable and infective through the air, both kinds of germs must be taken into account. It is not yet clear how the conjugation-germs spread through the system from the point of inoculation, but certainly they are diffused everywhere before the specific secreting vesicle is complete. Bryce's test shows that the system is affected enough to influence the course of a second vaccination in a new place, before the original vesicle is fully developed. Therefore, the full development of the latter is not the cause of the affection of the system. It is quite possible, also, that the morbid poison in the form of graft-germs may be inoculated and grow asexually in the spot for a time, even when the system is protected—thus showing the difference between graft-germ and conjugation-germ-action. This probably takes place often in revaccination, for the percentage of cases in which a vesicle is formed exceeds those of liability to a second attack of smallpox. Vaccinators do not like to use that matter, but its specific efficacy has not been disproved. It is said that the old inoculators of smallpox sometimes kept up a supply of matter on their own arms.

*

* Germinal Matter and the Contact Theory, by Dr. Morris, p. 67.

Similar principles apply no doubt to all the animal poisons which have a constitutional as well as a local action. Also the vegetable morbid poisons constituting Malaria must act as conjugation-germs, and the result of their union with the fixed or the blood plastids is no doubt an infertile hybrid, probably from the too great dissimilarity of the parent organisms. Hence the non-contagious nature of these diseases.

But it is impossible to pursue the subject further here, and I must be content to have given the above outline of an addition to Beale's graft-germ theory, and leave it to some future opportunity to follow out in detail the analogies of grafting, hybridization, need of intercrossing, etc., to the intricate processes involved in the infectious diseases. *

$25. In conclusion, let us pass again for a few minutes from matters of technical detail to the bearing of the principles here set forth on the general welfare of society, as affected by the fearful scourge of infectious diseases. The tendency of the foregoing has been to restore these diseases to the domain of medicine proper, in opposition to the parasitic hypothesis, fashionable for the moment, which would, as it were, consign them to a department of natural history. Were it so, there would be little hope of their extinction or mitigation by the medical art. On the other hand, if they are diseases bred within us from altered conditions of health, our prospects are better, though not unreservedly so. As long as infectious diseases, such as the catarrh and erysipelas group, arise from the operation of mere common non-specific causes, if by any chance they were swept clean out of the land, they would infallibly re

* In fact, the subject forms part of a work on "The Stimuli," with which I have been engaged for some years. I may also say that since the printing of this paper was finished I have found that Dr. James Ross had already noticed the analogy between disease-germs and the partial bions of Häckel, which is satisfactory as a corroboration of the views independently given here.

appear, so long as poverty, dirt, overcrowding, famine, war, vice, etc., afflict the human race.

We

And with respect to the diseases of the class which now never arise except from infection, and whose origin is hidden in the night of time, although we may circumscribe the area of their operation by such means, yet we can never hope that good food, virtue, drainage, and ventilation will extinguish them altogether as long as man is a social animal. That hope lies in the medical art, and, strangely enough, in the use of the very morbid poisons themselves whose tremendous power for evil has just occupied our attention. have already two examples of the marvellous perfection as medicinal agents of these incomparably powerful specifics; and as it is contrary to the continuity of nature that there should be exceptions to any laws, these instances cannot stand alone. Our hope for the future must therefore be, by diligent experiment and research, to extend the same principle to all the fixed infectious diseases. The two examples alluded to are, one of protection against disease by the wonderfully perfect operation of vaccination; the other of cure, viz., of Pannus, by inoculation with the virus of purulent ophthalmia. Of the former it is needless to speak, as its merits are universally acknowledged; but the latter is little known out of the medical profession, so it may be described more in detail.

The word Pannus, which means literally a cloth, is applied to an opacity and thickening of the cornea like a cloth, producing blindness. It is characterised by a superficial vascular opacity of the cornea, due to the formation of a layer of new-formed cells beneath the epithelium, and in the superficial layer of the cornea, which becomes thickened and its surface rough and irregular. It is attended with great injection of the blood-vessels and sensitiveness of the conjunctiva and globe of the eye in general, flow of tears, intolerance of light, and more or less complete blindness. It