MICROBIAL DISEASES OF MAN AND ANIMALS. 645 



the individual and the public are often effective in limiting and ending 

 an epidemic. 



While a great many sera have been used therapeutically with some 

 success, prophylaxis promises more where it can be widely employed as 

 in armies and navies. The artificial immunity is brought about by in- 

 jection of dead cultures. A difference of about 25 per cent has been 

 noted between the percentage of cases in vaccinated and unvaccinated 

 persons. 



ASIATIC CHOLERA.* 

 Microspira comma. 



The disease is endemic in parts of India whence epidemics have 

 spread throughout the world. America has been visited by several 

 epidemics and at the sea ports more frequently, chiefly New Orleans. 



The disease occurs naturally only in man. The incubation period 

 is from part of a day to ten days, usually about three days. 



In its most characteristic form the disease begins with few or no 

 prodromata. It is marked by fever, sudden onset of purging and vomit- 

 ing followed by cramps and severe depression. Evacuations finally 

 become almost a colorless liquid, " rice- water stools." The cramps may 

 occur in the whole muscular system most frequently in the legs and are 

 often extremely painful. A stage of complete collapse finally occurs. 

 There are, however, many variations from these typical cases. The mor- 

 tality is usually given at from 45 to 50 per cent. 



After death there is found extensive acute degenerative changes in 

 the kidneys; the gastro-intestinal tract shows marked changes in the 

 lining membrane which may be necrotic, sodden and in some places 

 stripped away. 



The cholera vibrios may sometimes be seen in enormous numbers in smears from 

 typical stools. For a positive diagnosis, however, the organism must be cultivated. 

 The usual method is to inoculate a i per cent peptone solution from the stool, incubat- 

 ng at 37 for from four to eight hours and sowing plates from the very surface of the 

 liquid, either a gelatin or alkaline agar or both. The vibrios are 3^ to 5^ long by 

 about 0.4^ wide, and are curved slightly like a comma or sometimes in a half circle 

 (Fig. 113). These comma forms are best seen in broth cultures. The ends are 

 usually rounded. In young cultures the organisms are usually arranged singly, occa- 

 sionally two may be found end to end in the form of an "S". There is no capsule, 



* Prepared by Edward Fidlar. 



