Page:Popular Science Monthly Volume 83.djvu/558

554 that the method was far from perfect. What in the method caused so great a variation?

An examination of animals that had died from small amounts demonstrated that death had been due to coagulation and to a consequent blocking of the blood stream. They then set about for a solution of the more serious problem—the prevention of coagulation. First, tests with various salts were made. But these were found to be of no service since a salt in order to be a non-coagulant had to be of sufficient strength itself to be toxic.

A second study hit upon an ingenious method of procedure. It has long been known that the blood of animals ingested by leeches is prevented from coagulation (in the body of the leech) by an anticoagulant. Haycroft demonstrated that an alcoholic extract of the buccal cavity of leeches injected into the arteries of rabbits or dogs prevents coagulation of the blood, and at the same time is productive of no observable injury. Joffroy and Serveaux determined upon testing its powers to prevent coagulation in a normal salt solution.

It is evident that the addition of so complex a substance as leech-extract to the blood of an animal must be made only with the most careful control. Two things were demanded of it: (1) It must serve its purpose,in this case prevent coagulation; (2) it must in no way injure the animal. In testing for its injurious effects it was found that the injection of enormous quantities produced no injury. Since no coagulation followed they were in possession of an anticoagulant by the aid of which they could test the toxicity of a substance added directly to the blood stream.

Joffroy and Serveaux established as a convenient unit of measure the amount of alcohol that would kill per kilogram while the experiment was in progress. This they called the experimental toxic equivalent. This limit, as is evident, has the advantage of greater rapidity than that (36 hours) used by Dujardin-Beaumetz and Audigé. By injecting the alcohol and this anticoagulant into the blood, in a series of eight experiments, the following amounts of alcohol were found sufficient to kill per kilogram of body weight: 12.65 c.c, 12.18, 11.69, 10.32, 10.51, 11.99, 12.48, 11.70. This series shows a striking regularity with extremes varying only between 10.32 and 12.65 c.c., variations which would be readily accounted for by differences in age, race and the like of the rabbits used.

For ethyl alcohol, then, these authors have demonstrated that 11.69