TOXINS. 19 



extends ; the neighbouring ganglions enlarge ; and the infection becomes 

 generalised. In the protected rabbit, on the contrary, the bacilli multiply at 

 tirst ; but soon the leucocytes arrive in such great numbers, that the microbes 

 are taken and killed ; the fluid in the swelling, instead of being clear, becomes 

 thick, cells are abundant it it, the bacilli disappear, the disease does not 

 extend, and it becomes cured " {Cadeac). 



Immunity may be acquired by the paralysing influence which the material 

 formed in the tissues by the disease germs, has on these microbes. Bouchard 

 has proved this in the cultivation of the bacillus of blue pus, and Raulin in 

 that of the aspergillus niger. As a familiar instance, Cadeac cites the experi- 

 ment of putting yeast in a solution of sugar, which mixture will produce 

 carbonic acid and alcohol. After a certain time the fermentation will stop. 

 If we add sugar to the liquid, the yeast will recommence growing ; but the 

 feimentation will soon again stop, and will not begin afresh even if we add 

 more sugar. If on the contrary, we add water, the fermentation will com- 

 mence again ; and will also do so, if by heating the liquid, we drive off the 

 alcohol which has been formed. In the first case, the effect of the water was 

 not to add to the materials necessary for the nutrition of the ferment, but to 

 dilute the matters formed by the yeast, of which alcohol was the principal. 

 In the second case, the heat expelled the alcohol or considerably diminished 

 it, and the fermentation commenced anew. Here, the alcohol has a poisonous 

 or paralysing efl'ect on the yeast which produced it. This theory may serve 

 to explain the fact that certain diseases, like contagious pleuro-pneumonia 

 and pink-eye (influenza), run a definite course, at the end of which, if the 

 animal has survived the severity of the symptons, the disease will disappear. 

 In this class of diseases, the acquired immunity will naturally be com- 

 paratively short-lived. The material which Pasteur employed for innoculation 

 as a preventive to rabies, and which is obtained from the spinal cord of rabid 

 rabbits, may act in the same manner, by checking the development of the 

 microbe that is supposed to produce rabies. 



Behring and Kitasato have shown that the serum (the watery portion of the 

 blood) of animals which have had respectively diphtheria or tetanus, and the 

 serum of animals which are immune to these respective diseases, are antidotes 

 to these complaints. 



In seeking for an explanation of this phenomenon, we naturally 

 turn to the fact that the microbes of diphtheria, tetanus, glanders, and other 

 diseases act injuriously on the system of an affected animal by means of the 

 poisons {toxins) which they or their respective ferments manufacture in the 

 animal body. These toxins are chemical poisons of extreme virulence : 

 for instance, two drops of tetanus toxin will kill a horse. Behring and 

 Kitasato argued that the immune serum produces its effect by reason of its 

 containing a substance (anti-toxin) which has the power of neutralising or 

 rendering inert its respective toxin, probably by combining chemically with 

 it. Roux, however, has shown that, although a mixture of tetanus toxin 

 (for example) and immune serum, on being injected, produces no ill effects 

 on a healthy animal ; it causes the death by tetanus of animals whose systems 

 are under the influence of certain microbic diseases, such as strangles, which, 

 it is almost needless to say, diminish the resistance of the tissues. Further, 

 we have the theory that immune serum produces its protective effect by 

 stimukting the system to resist the action of the toxin. In accordance with 

 this view, we have the fact (p. 15) that in inflammation, the leucocytes and 

 cells of an injured part absorb and digest dead and effete matter. 

 Metchnikoff has also proved that the leucocytes and cells of the tissues, both 

 of which he classes under the heading of phagocytes, perform a like office in 

 contagious diseases by absorbing into their substance, and by digesting, the 

 attacking microbes. Here we again return to Metchnikoff's idea of protection 

 being obtained by the training of the phagocytes. Calmette has made 

 animals immune from the bites of certain poisonous snakes by repeated in- 

 jections of the venom, in, at first, small (non-lethal) doses which were 

 gradually increased, without injuriously affecting the patient, to many times 



2* 



