TOXINS. 19 



been protected by vaccination, behold what we may observe at the respec- 

 tive seats of inoculation. In the ordinary rabbit, the microbes multiply 

 rapidly. The swollen part is full of watery fluid, and is poor in cells. 

 Little by little the swelling extends ; the neighbouring ganglions enlarge ; 

 and the infection becomes generalised. In the protected ra)bbit, on the 

 contrary, the bacilli multiply at first ; 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 in it, 

 the bacilli disappear, the disease does not extend, and it becomes cured " 

 (Cadiac). 



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 

 experiment of putting yeast in a solution of sugar, which mixture will pro- 

 duce 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 fermentation 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 commence 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 oommenced anew. Here, 

 the alcohol has a, poisonous or paralysing effect 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 

 symptoms, the disease will disappear. In this class of diseases, the acquired 

 immunity will naturally be comparatively short-lived. The material which 

 Pasteur employed for inoculation 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. 



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) wliich they or their respective ferments manufacture in the 

 animal body. These toxins are chemi<;al poisons of extreme virulence ; 

 for instance, two drops of tetanus toxin will kill a horse. 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. 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 microbio 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 pro- 

 tective effect by stimulating the system to resist the action of the toxin. 

 In accordance with this view, we have the fact (p. 15) that in inflaramartion, 

 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 oflSce in contagious diseases by absorbing into their substance, and 

 by digesting, the attacking microbes. Here we again return to Metchni- 

 koff's idea of protection being obtained by the training of the phagocytes. 



2* 



