PROGRESS OF MICROSCOPICAL SCIENCE. 231 



These solutions were now used in the control-experiments. 



For instance : 



a. Principal experiment. 100 c.c. salt solution,* 2 grms. glucose, 

 • 3 grm. peptone boiled and treated in' the ordinary manner.| On 

 the third day the liquid contains countless swarms of bacteria. 



6. Control-experiment. 100 c.c. salt solution, 1 grm. glucose, 

 0-5 grm. urea, boiled exact. No bacteria appear; on the eighth day 

 the liquid is perfectly clear. 



c. Control-experiment. 100 c.c. salt solution, 0*5 grm. peptone, 

 boiled, &c. On the eighth day complete absence of bacteria. 



In each of these experiments the reaction is neutral. They are 

 therefore fully comparable. The experiments h and c prove, more- 

 over, that the closing tiles exclude completely the atmospheric germs, 

 a fact that was also proved by direct experiments, wherein the solu- 

 tions 6 and c were used aud dust strewn on the closing tile in the 

 manner formerly described. 



But is it not possible to generate bacteria in a liquid which has 

 been boiled when acid ? 



To elucidate this point, the above-named solution a was rendered 

 acid (2-4 c.c. of a 1 per cent, solution to 100 c.c.) and treated as 

 usual. No bacteria appeared, whether the liquid was, after boiling, 

 neutralized with soda or not. 



But this negative result is easily conceivable ; for the acid alters 

 essentially the calcium-phosphate, changes CaHPO^ into C^HjP^On. 

 And that this alteration is not without influence, is rendered probable 

 by the fact, which I have recorded in the ' Maandblad voor Natuurwe- 

 tenshcappeu,' No. 7 (April 23, 1873), namely, when in the principal ex- 

 periment instead of CaHP04is used a mixture of CasP-^Oj, aud Ca^H^P^^Oj, 

 the result (the genesis of bacteria) is much less constant. The neutral 

 calciimi-phosphate by boiling with water breaks up in the basic and 

 the acid salt, but this division must take place in the presence of 

 sugar and peptone. On the other hand, the acid modifies the peptone. 

 This is easily demonstrated by comparing, in the polariscope, the ro- 

 tating power of a neutral peptone solution with the power of the same 

 solution. After boiling with acid a notable difference is observed. 



The acid can, nevertheless, be employed with the foUomng modi- 

 fication : — In 100 c.c. water are dissolved 0*2 grm, potassium-nitrate, 

 • 2 grm. magnesium-sulphate, and 2 grms. glucose ; 2 c.c. of a 1 per 

 cent, solution of tartaric acid are added, so that the liquid has a strong 

 acid reaction. It is then boiled for ten minutes. Then with a red- 

 hot platinum spatule a little soda is taken from a hot crucible and 

 thrown in the flask. The quantity of soda required is approximately 

 ascertained by a preliminary trial. Care should be taken not to render 

 the liquid alkaline. Then • 05 grm. calcium-phosphate and • 3 grm. 

 peptone are added together, and the boiling continued for ten minutes. 

 The flask is closed as usual, and deposited in the hatching-bath. Three 

 days after, it swarms with bacteria. 



* Composed of 1 grm. potassium-nitrate, 1 grm. magne^uim-sulphate, 0"2 grm. 

 neutral calcium-phosphate in 500 c.c. water, 

 t See 'Nature,' vol. vii., p. 380. 

 VOL. X. T 



