ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 585 



the preliminary beating has destroyed the anti-try ptic power of the meat 

 juices, rapidly breaks down some of the albumins present. The trypsin 

 is allowed to act for from two to three hours, the temperature being kept 

 raised by placing the vessel containing the mixture in an incubator at 

 37° C. The next process is to precipitate the unaltered albumins and 

 to render the broth easily filtrable, and with this in view the mixture is 

 rendered slightly acid with acetic acid and brought to the boil. The 

 coagulated proteids and other solid matters can now be almost entirely 

 separated by straining through a bag of close-meshed muslin. 



After rendering the fluid thus obtained alkaline to litmus, a small 

 quantity of calcium chloride (about ■ 5 grm. to the 4 litres) and ■ 25 p.c. 

 of sodium chloride are added, and the resulting broth is then autoclaved 

 for an hour at 115 C.° so as to precipitate thoroughly any phosphates 

 that may be in solution, filtered through filter paper, and then tubed 

 and sterilized as in the case of ordinary peptone broth. In making agar 

 the agar powder is best added before the phosphates are precipitated, as 

 the prolonged heating brings the agar thoroughly into solution. 



This medium has the following advantages over that made from 

 beef extracts and prepared peptones :— 1. The cost is very much less. 

 2. The growth of the bacteria both on the solid and liquid forms has 

 proved to be very much more abundant than that obtained on the media 

 usually employed : for instance, it has been found that four times more 

 typhoid bacilli were obtained from agar bottles in a given time contain- 

 ing medium thus made than in the case of medium made from beef 

 extract and Witte's peptone. 



Peptone-free Medium for the Cultivation of the Tubercle 

 Bacillus.* —The medium, the preparation of which is described by 

 S. R. Douglas, was the outcome of the following observations. In the 

 first place, it was noticed in cultivating tubercle bacilli on glycerin 

 potato, that frequently an abundant growth of the tubercle bacillus 

 occurred on the surface of the glycerinated salt solution which was 

 contained in the lower part of the tube. Attempts were therefore 

 made to make a broth from potatoes which would give a good growth 

 of such bacilli. On such a broth good growths were frequently obtained, 

 but from time to time an individual brew gave but unsatisfactory 

 results. These unsatisfactory results seemed to rest with some quality 

 of the potatoes rather than with any variation of alkalinity, etc. Noting, 

 however, that the tubercle bacillus seemed readily to assimilate even 

 coagulated albumin, it was determined to try the effect of adding some 

 form of soluble albumin, unaffected by the temperature necessary for 

 the sterilization of the broth, and with this in view various casein 

 preparations on the market, sold under patent names, were tried in order 

 to ascertain if these, when added to the extract of potatoes, would ensure 

 a medium giving constant and abundant growth of the tubercle bacilli. 

 The preparation giving the most satisfactory results was that sold under 

 the name of " Plasmon." 



The medium is made in the following manner. Potatoes are 

 skinned, then passed through a mincing machine, and the resulting pulp 



* Lancet, 1914, ii. p. 892. 



