20 DE. E. KLEIN. 



and it is therefore necessary to take one's chance, so to speak, 

 of having a number of failures owing to accidental contamina- 

 tion. And it is this very point, viz. the chance of contamina- 

 tion with air organisms, which makes the Koch's method, as 

 recommended by him, impracticable in the case of many culti- 

 vations, as I shall have to point out below in detail. 



It depends very much on the place and season where and 

 when the charging is carried out, as regards the accidental 

 contamination with air organisms. I have made some com- 

 parative studies on these points, and 1 think it worth while to 

 enter here more fully into them. 



At first, when working at the laboratory of St. Bartholo- 

 mew's Hospital Medical School, I charged my test-tubes from 

 my stock flask under carbolic-acid spray, the carbolic acid being 

 of the strength of about 5 — 6 per cent. From my note-book I 

 gather that in one series I charged sixteen test-tubes carefully 

 under the carbolic-acid spray, and placed them into the incu- 

 bator at about 35° C. Of these test-tubes one went bad in 

 the course of twenty-four hours, at which time it became 

 turbid owing to the presence of actively moving bacilli. In 

 another series of fourteen test-tubes two went bad. In a 

 third series of twenty-two test-tubes every one went bad, 

 although the method of charging under the carbolic-acid spray 

 was the same as in the other cases ; but the conditions of the 

 atmosphere were not the same. While I had tolerably good 

 results in July and August I had very bad results in October, 

 and my failures, both in preserving sterile my stock fluids and 

 my test-tubes charged with them, became during this month so 

 numerous and persistent that I had to give up work altogether 

 for this period. To have cultivations exposed to the air and 

 not afterwards sterilised, as is almost the general rule in Koch's 

 method of gelatine cultures, and to keep them pure was alto- 

 gether out of the question. The cause of these universal and 

 unconditional failures was not far to seek. During October 

 we had a good deal of dry weather with strong winds, and the 

 laboratory in which I worked faces Smithfield hay market, 



