HYDROPHOBIA. 



485 



treated in fourteen days, which goes to prove 

 that the real incubation-period of canine ra- 

 bies is about fourteen days. On trying the ex- 

 periments with rabbits, it was found that the 

 period of canine rabies in rabbits is also four- 

 teen days. It then occurred to Pasteur to try 

 similar experiments on monkeys, on account 

 of their zoological connection with the human 

 species. The results of these experiments were 

 very astonishing. There was no development 

 of any of the phenomena of rabies, or hydro- 

 phobia, in the manner expected; the symp- 

 toms were much milder than in dogs, rabbits, 

 or human beings. As experimentation with 

 the etiological elements in some other diseases 

 had shown that in some animals they either 

 augmented or decreased in virulence by being 

 passed through several animals of a given spe- 

 cies, Pasteur resolved to try this with monk- 

 eys, and found that it was only necessary to 

 pass rabid material from monkey to monkey, 

 through a very small number, in order to have 

 it entirely lose its virulence. Here was an op- 

 portunity to procure a " primary " or weak 

 vaccine, had it not been impossible from the 

 scarcity and high price of monkeys. Rabbits 

 were again resorted to, and, after trying hun- 

 dreds of them, it was found that a form of 

 rabies was produced which had a regular pe- 

 riod of incubation of but seven days. It is 

 necessary again to call to mind the fact that, 

 in canine rabies, this period is of fourteen days' 

 duration, because, if hydrophobia should fol- 

 low the preventive treatment of Pasteur in a 

 human being, if it is due to the bite from the 

 dog, by inoculating a dog or rabbit with brain- 

 substance from said person, the animal inocu- 

 lated would show the characteristic symptoms 

 in fourteen days or thereabout, while if due to 

 the inoculated virus the disease would appear 

 in the animal in about seven days. 



The next question is, How can this very 

 virulent rabbit material be made less virulent, 

 until a negative condition is obtained, so that 

 it can be safely used as a virus for preventive 

 inoculation ? Experience has shown that heat 

 and the action of the oxygen in the air had fre- 

 quently produced this effect with other forms 

 of virus. As the cerebral substance is not in a 

 convenient shape for such manipulation, the 

 medulla oblongata offered itself as the nearest 

 portion of the cord to the brain, as well as the 

 easiest portion to be got at. It was also neces- 

 sary to have some way of removing or absorb- 

 ing the moisture as rapidly as possible from the 

 nervous material. To this end, glass jars, hold- 

 ing about a quart, with the finest and closest 

 fitting corks, are necessary ; and they must be 

 carefully washed and sterilized. Each jar is 

 then filled about one third with the driest of 

 caustic potash, in lumps, which on account of 

 its affinity for moisture absorbs all that may 

 be in the air and that in the nerve-substance. 

 In each jar is then hung, from the bottom of 

 the cork, by a thread, the medulla oblongata 

 from a rabbit that has died of rabbit rabies. 



When the jars are placed in a very cool room, 

 the nervous substance retains its virulence for 

 a long time, which may be increased by filling 

 the jars with carbonic-acid gas. On the other 

 hand, if the jars are placed in a room having a 

 constant temperature of 20 0., the medullas 

 will be found to lose in virulence, until at the 

 end of about fourteen days such changes have 

 taken place in the medullary substance that 

 inoculations with it in the sub - membranal 

 space of rabbits' or dogs' brains are not fol- 

 lowed by any perceptible effects. 



Medullas thus treated give us, then, a " pri- 

 mary vaccine " that can be used in prevent- 

 ive inoculation. If we take 100 medullas, 

 representing an equal number of rabbits that 

 have perished from the seven-day or rabbit 

 rabies, and subject them all to this treatment, 

 we shall find that each medulla has approxi- 

 mately the same degree of virulence, if they 

 have been subjected to the action of the hot 

 dry air for the same number of days. The re- 

 sults of hundreds of experiments prove the cor- 

 rectness of this statement. If we take a given 

 number of dogs and treat them for ten days 

 with a virus made from cords that have been 

 treated in the above-described manner, and per- 

 mit a month to elapse in order to satisfy our- 

 selves that inoculated or rabbit rabies is no 

 longer possible, and then permit these same 

 dogs to be bitten by known rabid dogs ; and if 

 we take another given number and treat them 

 in the same preventive manner, allowing a simi- 

 lar period to elapse, and inoculate them with 

 fresh medullary substance from rabbits that 

 have died of rabies we shall find that the dogs 

 in each case remain perfectly free from any 

 outbreak of rabies. If at the same time we 

 take brain-substance from the rabid dogs that 

 we allowed to bite the inoculated ones, or a 

 portion of the medullary substance from the 

 rabid rabbits that we used for the test inocu- 

 lations, and again inoculate healthy dogs or 

 rabbits as a control experiment, we shall find 

 that these animals will invariably die in either 

 seven or fourteen days, according to the mate- 

 rial used. The same will be found to be the 

 case if we take the same number of non-inoc- 

 ulated, healthy dogs and permit the same rabid 

 dogs to bite them that we used in the first ex- 

 periment ; the non-treated dogs will all die of 

 rabies in course of time. 



The same method of treatment has been 

 found of equal value in preventing the outbreak 

 of hydrophobia in human beings, if it is resort- 

 ed to within ten or even twenty days from 

 the time they were bitten. After that period 

 it is not reliable. For grown persons an entire 

 syringeful is used ; for children under fourteen 

 half as much. The substance is not introduced 

 into the brain, but under the skin, in the same 

 manner as a solution of morphine. The pro- 

 cedure is best illustrated by quoting from the 

 ** Comptes Rendus V of October, 1885. 



The first person treated by Pasteur was the 

 Alsatian boy, Joseph Meister, aged nine, and 



