180 Mr. J. A. Craw. On the Physical [Mar. 22, 
from cultures of B. megathertwm, and succeeded in producing a very strong 
antilysin for the same. He demonstrated that, in constitution, this lysin 
resembled tetano-lysin and diphtheria toxin. JI, therefore, determined to test 
in how far the various views were applicable to the relations existing between 
Megatherium lysin and antilysin. Dr. G. Dean kindly placed the antilysin 
prepared by Dr. Todd at my disposal. I here beg to express my deep sense 
of indebtedness to Dr. G. Dean for his kindly criticism and many suggestions, 
and to Dr. C. J. Martin for his counsel in the filtration experiments. 
On the hemolytic index employed—That the heemolytic effect is always 
proportional to the amount of lysin added seems to be more than 
doubtful, consequently the calculated concentrations of free lysin have not 
been given. : 
However, when the hemolytic powers of two solutions of the same lysin 
in the presence of a considerable concentration of antilysin are not widely 
different, the powers are approximately proportional to the amounts of free 
lysin present. The hemolytic power of a fluid was determined by adding 
1 ce. to 2 cc. of a 2°5-per-cent. suspension of washed guinea-pig 
corpuscles in 0°8-per-cent. saline, and heating the mixture to 37° C. for three 
hours. 
The contents were subsequently allowed to stand in the ice-chest until the 
corpuscles had sedimented sufficiently to allow of 1 c.c. of the supernatant 
fluid being removed. The intensity of colour of the fluid was then compared 
with that of the tinted scale of a von Fleischl’s hemoglobinometer. By 
using a disc of paper stained with potassium chromate, instead of the usual 
white illumination, the contrast in colour between hemoglobin and scale is 
much diminished, and daylight may be used for the comparison. Only that 
portion of the scale between the numbers 30 and 70 was used, and when the 
fluid was strongly coloured, dilutions were made so as to bring the final tint 
within these limits. The scale was standardised by various dilutions of the 
fluid obtained when 1 c.c. of lysin completely hemolysed 2 cc. of 2°5-per- 
cent. corpuscles in saline. The intensity of tint of this fluid has been repre- 
sented by the index 100, and the hemolytic indices given below refer to this 
tint as a standard. The experimental error in determining the tint was found 
to be less than 1 per cent. of the standard tint. 
In the following a “ partially neutralised ” mixture of lysin and antilysin 
is a fluid giving a marked hemolysis under standard conditions ; a “neutral” 
mixture gives no hemolysis in three hours, but would hemolyse slightly in 
four hours; an “ over-neutralised ” mixture contains a greater proportion of 
antilysin than a neutral mixture. 
