84 The Precipitins : Methods 



way. Three series of 11 tubes were prepared, each containing '5 c.c. of 

 a 1 in 21 dilution of human serum in salt solution. To the first tube 

 were added 5 drops of a solution of acid, to numbers 2, 3, 4 and 5 were 

 added 4, 2, 3 and 1 drops of acid respectively. The sixth tube was not 

 treated in any way. Numbers 7 to 11 received 1 to 5 drops of alkali 

 respectively. 



In the first series very small drops of a 1 in 100 dilution of 

 hydrochloric acid was used, in the second series large drops of the same 

 solution, and in the third series large drops of 1 in 10 solution of the 

 same acid. Large drops of corresponding dilutions of sodium carbonate 

 were used in series two and three. 



In the quantitative experiments - 1 c.c. of anti-human serum was run 

 into each tube, and in the qualitative one drop. 



Series I. Series II. Series III. 



No. of tube Drops Small drops % Large drops /o 



jail (0%) 



1 in 10 



Hydrochloric 

 Acid 



1 in 10 



Sodium 



Carbonate 



0516 (100%) 

 0169 (31,,) 

 0150 (29,,) 



tr ? 



nil (0/ ) 



In series II the acidity and alkalinity varied from about 1 1000 to 

 1 5000 and in series III from about 1 100 to 1500. 



These experiments show that the presence of even small quantities 

 of acid or alkali rapidly reduce the quantity of precipitum formed 

 (see Plate, fig. 5). The apparent exceptions of numbers 10 and 11 of 

 series II are due to the fact that the precipita produced were more 

 flocculent and occupied more space than the more compact precipita 

 elsewhere obtained. They also indicate that the presence of small 

 quantities of acid or alkali do not alter the specificity of the reaction, 

 for controls with anti-sheep serum were all negative. 



Qualitative experiments undertaken on the same lines showed that 

 with 1 in 100 solutions of acid and alkali, cloudings first occurred in the 

 normal tube, next in the alkaline series, the times of their appearance 

 increasing from No. 6 to 11. The last two showed faint traces of the 

 specific reaction and also general opacity. On the acid side cloudings 

 due to the acid rapidly appeared, but later specific cloudings were 



