ULTRA-MICROSCOPIC OR FILTERABLE VIRUSES 261 



is a frequent experience, and does not necessarily imply 

 that this organism bears an etiological relation to the disease 

 from which the individual may be suffering (see Staphylococcus 

 Epidermis Albus). 



When more than a few drops of blood are needed, as may 

 be the case in deciding the general nature of an infection 

 process, it is customary to withdraw it from one of the super- 

 ficial veins of the forearm by means of an hypodermic 

 syringe. The operation should be done under strictly 

 asceptic conditions, i. e., the skin should be thoroughly 

 cleaned with soap, water, and alcohol; the hands of the 

 operator should be surgically cleaii; the syringe must have 

 been sterilized immediately before using, and great care 

 should be taken that no air bubbles be injected into the 

 veins during the operation. 



In interpreting the results of cultures made from blood 

 drawn in this manner, the possibility of contamination by 

 skin bacteria should not be forgotten. The success of the 

 operation depends upon attention to the most minute 

 details of aseptic practice. It requires for its safe practice 

 skill in manipulation, experience and judgment in the inter- 

 pretation of the results. It is not, therefore, an operation 

 to be commended to the beginner. 



"ULTRA"-MICROSCOPIC OR "FILTERABLE" VIRUSES. 



These terms relate to particular substances capable of 

 causing disease, that are so small as to be beyond the visual 

 range of the microscopes used in bacteriological work, which 

 do not respond to the usual methods for the cultivation of 

 bacteria and which are able, because of their minute dimen- 

 sions, to pass through the pores of the finer grades of earth- 

 enware filters. 



