96 31anual of Veterinary Microhiologyi. 



ble products produced by pathogenic bacteria. These 

 vaccinating substances are known for a certain num- 

 ber of diseases — the pyocyanic disease, bacteridian 

 charbon and symptomatic charbon, cholera, Pasteur's 

 septicaemia, pneumo-enteritis of the pig, rabies, hu- 

 man tuberculosis (Koch's lymph will give immunity 

 to guinea pigs), tuberculosis of birds (Courmont and 

 Dor have vaccinated the rabbit by means of the solu- 

 ble products of cultures), etc. 



These substances, also called chemical vaccines, 

 have a great advantage over the figured elements; 

 the attenuated virus may indeed, in exceptional cases, 

 regain its virulent properties, and this unknown to 

 the experimenter; it then produces the fatal disease 

 instead of the immunity which was expected of it. 

 The soluble vaccinating substances, however, are not 

 entirely free from danger; they are nearly always 

 extremely violent poisons, and the quantities em- 

 ployed must be judiciously regulated. The discovery 

 of these substances is of such recent date that in 

 practice we have Jiot as yet reaped the benefits from 

 them which we may reasonably expect. 



Attempts at the prevention and cure of the mi- 

 crobic diseases by organic liquids coming from species 

 naturally refractory to these diseases have been made 

 in recent times; here, again, the action concerned is 

 a chemical one. The blood of the goat, transfused 

 to the rabbit at the time that the latter is inoculated 

 with tubercular products, will prevent the evolution 

 of tuberculosis; if the transfusion is made after the 

 disease has already commenced, it will retard it and 

 may even cause its retrogression. 



Injection of the blood serum of the dog (haemocyne) 



