1008 RECORD OF CURRENT RESEARCHES RELATING TO 



viduals, is sufficient to cause tlieir death ; and tliis is doubtless the 

 manner in which this disease is spread through the fowls inhabiting 

 any one yard. The isolation of the sick from the sound birds, 

 together with the most careful cleansing of the yard and the mainte- 

 nance of it in a clean state, will certainly suffice to put a stop to the 

 spread of the malady. 



The repeated cultivation of the microbion in fowls'-broth by im- 

 pregnating each successive liquid with an infinitely small quantity of 

 the preceding liquid, weakens in no degree the poisonous properties of 

 the agent. Its virulence is so great that inoculation by a very small 

 portion of a drop of one of the growths thus reared causes death in 

 every instance within two to three days, and very often within twenty- 

 four hours. It is possible by certain modifications of the method of 

 cultivation to bring about a mitigation of this virulence. The occur- 

 rence of this mitigation is marked by a slight retardation of the 

 development of the microbion, " but in reality the two kinds of 

 poison are identical. In the first, the most deadly condition, the 

 microbion may cause death twenty times in twenty cases of inocula- 

 tion ; in the second, out of twenty cases of inoculation it causes 

 twenty cases of disease, but never death. These facts have an 

 importance which is readily apjireciable ; they allow us, in fact, 

 to decide the problem of the recurrence or non-recurrence of the 

 disease now in question. If we take forty fowls and inoculate 

 twenty of them with a very poisonous specimen of infecting material, 

 the twenty fowls die ; if we inoculate the remaining twenty with 

 weakened poison, they become one and all ill, but will not die. If 

 we now let them become well again, and inoculate these twenty fowls 

 with the most poisonous substance, it will now no longer kill them. 

 The conclusion to be drawn from this is clear ; the malady is a safe- 

 guard against itself. It has the characters of the infectious diseases, 

 which do not recur." 



At this point M. Pasteur reminds us that, of course, this fact is of 

 itself nothing new, for man has long been successfully protected against 

 small-pox by inoculation with cow-pox, the sheep in some places 

 against hoof-disease, the cattle against the rinderpest, and it is also 

 well known that people who have passed through measles, scarlet 

 fever, syphilis, &c., are not again attacked by these diseases. The 

 new and important point about the cholera of fowls is this, that we 

 have found the infecting agent in this disease to consist of a micro- 

 scopic parasite, which may be cultivated outside the body, and which 

 not only evokes the disease, but also affi^rds immimity against the 

 effects of a repeated inoculation as distinctly as the contagious 

 diseases. 



The following passage of M. Pasteur's memoir qualifies slightly the 

 conclusion arrived at above : — 



" I do not wish to have it believed that the facts present the mathe- 

 matical exactness and regularity which I have described. That is, my 

 statements do not take account of the great variability which is acci- 

 dentally presented by the constitutions and general vital powers of 

 individuals taken from a collection of domestic animals. No, the most 



