x MODES OF DESTRUCTION OF B. PESTIS 283 



presently, supply an absolute guide for the application of the dis- 

 infectant in actual practice. In practical life a disinfectant is 

 applied by a surgeon, by the sanitarian, or by the nurse, not to an 

 artificial culture or to an emulsion of an artificial culture, but to 

 materials, such as excretions, secretions, morbid products, and 

 morbid tissues, derived directly or indirectly from the human or 

 animal bodies. The microbes to be acted upon by the disinfectant 

 are embedded in, surrounded by, and mixed with various materials. 

 This condition cannot obviously be compared with that of a microbe 

 in a broth culture, or with a watery or salt emulsion of the growth 

 taken from an artificial culture. The surgeon who wishes to disinfect 

 a wound and to keep it antiseptic has to apply the disinfectant to 

 tissues and not to a watery emulsion ; the nurse who is supposed to 

 disinfect a typhoid stool with a given disinfectant is not acting on a 

 watery or saline emulsion of a culture of the typhoid bacillus, but 

 on materials of a highly complex composition, and altogether of a 

 different nature from the laboratory culture. 



An illustration is sufficient to prove the difference between the 

 one kind of disinfectant and the other. Staphylococcus pyogenes 

 aureus (of a recent and active culture) is justly considered one of the 

 hardiest non-sporing microbes, at any rate as far as chemical disin- 

 fectants are concerned, and for this reason bacteriologists are in the 

 habit of using this microbe in their laboratory tests. 



Now, the Staphylococcus aureus, taken from a culture (broth or 

 agar) and placed into a watery solution or distributed in a disinfectant, 

 is by simple agitation in most cases readily emulsified ; the fluid 

 viewed under the microscope shows the microbes almost uniformly 

 distributed as single cocci or as diplococci or as very small groups. 

 Compare with this a microscopic specimen of the contents of an 

 abscess or of the secretion of a wound or ulcer. Here we find, 

 besides crowds of various tissue elements, leucocytes, debris, tissue 

 fibres, fatty granule-cells, etc., large and small clumps of cocci and 

 diplococci not only in the fluid menstruum, but within the protoplasm 

 of leucocytes, within debris, and within masses of fibres. 



The disinfectant which is to act on the microbe so surrounded 

 and lodged has a task to fulfil quite different from what it has when 

 it is added to a broth culture or other uniform emulsion of the microbe. 

 The same, mutatis mutandis, applies to diphtherial membrane, to 

 sputum, to the typhoid stool, and other animal excretions. In the 

 following experiments I wish to show by direct observation that in a 



