104 THE AMERICAN MONTHLY [Apr., 



equal fairness to say, as far as he can how much allow- 

 ance should be made for these exceptions, — what percent- 

 age of chance there may be that he is mistaken. Some 

 incomplete tables show that the possibilities, that the 

 corpuscles of a dog's Idood would measure as much as 

 those of a man, are about one in sixty- two. As against 

 all other common domestic animals the probability of 

 error is much less. The subject is an interesting one, it 

 is much too large to be condensed into a small space. 

 Much of the work already done is unreliable, and I hope 

 that this paper will have the effect of calling the atten- 

 tion of microscopists again to the matter, and of doing 

 something toward stimulating the present uncertainty, 

 and giving some facts which can be accepted beyond 

 question. 



Formalin in Bacteriology, with More Especial Reference to 

 its Action on the Bacillus of Diphtheria. 



By dr. W. W. ALLEGER, 



WASHINGTON, D. C. 

 [Kead betbre the Microscopical Society of Washingtou, Jau. 9, 1894.] 

 Formalin is the proprietary name of a 40 per cent solu- 

 tion of formic aldehyde recently put upon the market by 

 Schering, of Grermany. Formic aldehyde is a gas having 

 the composition CH9O. According to Roscoe and Scho- 

 rlemmer it was first successfully prepared by Hofman 

 in 1867 by passing the vapor of methyl alcohol (wood 

 spirit), together with air, over ignited platinum wire : it 

 is also known as the oxide of methene and as the aldehyde 

 and ketone of formic acid. 



So far as I am aware formic aldehyde has been put to 

 no practical use prior to the manufacture of the concen- 

 trated solution by Schering; and little is yet known of its 

 properties aside from the information contained in the 

 circular issued by him. 



