344 BACTERIOLOGY. 
kidneys. The number of leucocytes in the blood is in- 
creased. From the area surrounding the point of inocu- 
lation virulent bacilli may be obtained, but in the in- 
ternal organs they are only occasionally found, unless an 
enormous number of bacilli have been injected. Paral- 
ysis, commencing usually in the posterior extremities 
and then gradually extending to other portions of the 
body and causing death by paralysis of the heart or 
respiratory organs, is also produced in many cases in 
which the inoculated animals do not succumb to a too 
rapid intoxication. In rare instances the muscles of 
the neck or of the larynx are first paralyzed, and thus 
characteristic symptoms are caused. In a number of 
animals I have seen recovery take place three to six 
weeks after the onset of the paralysis. 
Diphtheria Toxin. It is evident that a micro organ- 
ism which, when injected subcutaneously, destroys the 
life of susceptible animals and produces such marked 
anatomical changes in the internal organs, while it is 
found only at or near the point of inoculation, must 
owe its pathogenic power to the formation of a poison 
which, being absorbed, gives rise to toxemia and death. 
This poison or toxin bas been partially isolated by Roux 
and Yersin, and others, by filtration through porous 
porcelain from cultures of the living bacilli. It has not 
yet been successfully analyzed, so that its chemical 
composition is unknown, but it has many of the prop- 
erties of proteid substances, and can well be designated 
by the term active proteid (see page 72). Diphtheria 
toxin is totally destroyed by boiling for five minutes, 
and loses some 95 per cent. of its strength when ex- 
posed to 75° C. for the same time; 73° C. destroys 
only about 85 per cent. and 60° very little. Lower 
