72 POISONS : THEIR EFFECTS AND DETECTION. [§ 42 . 
Neumann affirms that the pattern which the fibrin or coagulum of 
the blood forms is peculiar to each animal, and Dr Day, of Geelong, 
has independently confirmed his researches : this very interesting 
observation perhaps has not received the attention it merits. 
When there is sufficient of the blood present to obtain a few milligrms. 
of ash, it may be possible to distinguish human blood from that of other 
common mammals by estimating the relative amounts of potassium 
and sodium in the blood. In the blood of the cow, sheep, fowl, pig, 
and horse, the sodium very much exceeds the potassium in the ash ; 
thus the proportion of potassium oxide to that of sodium oxide in the 
blood of the sheep is as K 2 0 : Na 2 0 : : 1 : 6 ; in that of the cow, as 1 : 8 ; 
in that of the domestic fowl, as 1 : 16 ; while the same substances in 
human blood are sometimes equal, and vary from 1:1 to 1 : 4 as 
extremes, the mean numbers being as 1 : 2-2. The potassium is 
greater in quantity in the blood corpuscles than in the blood serum ; 
but, even in blood serum, the same marked differences between the 
blood of man and that of many animals is apparent. Thus, the pro¬ 
portion of potash to soda being as 1 : 10 in human blood, the proportion 
in sheep’s blood is 1 to 15-7 ; in horse’s serum as 1 to 16*4 ; and in the 
ox as 1 to 17. Since blood, when burnt, leaves from 6 to 7 per 
thousand of ash, it follows that a quantitative analysis of the relative 
amounts of potassium and sodium can only be satisfactorily effected 
when sufficient of the blood is at the analyst’s disposal to give a weigh- 
able quantity of mineral matter. On the other hand, much work 
requires to be done before this method of determining that the blood is 
either human, or, at all events, not that of an herbivorous animal, can 
be relied on. We know but little as to the effect of the ingestion of 
sodium or potassium salts on either man or animals, and it is possible— 
nay, probable—that a more or less entire substitution of the one for 
the other may, on certain diets, take place. Bunge seems in some 
experiments to have found no sodium in the blood of either the cat or 
the dog. 
The source from which the blood has emanated may, in a few cases, 
be conjectured from the discovery, by microscopical examination, of 
hair, or of buccal, nasal, or vaginal epithelium, etc., mixed with the 
blood-stain. 
§ 42a. Biological Test for Human Blood.— A test for distinguishing 
human from animal blood has been devised by Jules Ogier and 
Herscher. 1 The blood-spot is dissolved in water, and two or three cubic 
centimetres of the solution are placed in test tubes 10 to 12 cm. long 
and 4 to 5 cm. diameter. In similar tubes is placed the same quantity 
of control solutions of human, pigs’, oxen’s, dogs’, or other blood, of 
approximately the same strength. 
1 Anti. Chim. Anal., 1902, vii. 241. 
