5« 



SCIENTIFIC NEWS. 



[Nov . i6, if 



taining some useful tables, and a description of the more 

 interesting fixed stars, etc., contained in the maps. We 

 can strongly recommend this atlas to those of our 

 readers who are interested in astronomy. 



RECOGNITION OF HUMAN BLOOD. 



""pHE diagnosis of human blood, as distinguished from 

 -*• that of the lower animals, is often an important 

 point of criminal jurisprudence, when blood-stains on 

 garments or weapons are laid before the courts as 

 evidence. 



This difficult question has lately been discussed in the 

 Journal of Comparative Medicine, by Dr. H . Formad . 



For deciding the general question whether a certain 

 stain is due to blood or to some vegetable juice or artifi- 

 cial dye the spectroscope and various chemical reagents 

 come into play. But to prove that a given specimen of 

 blood is human or otherwise the microscope alone is of 

 any value, and the sole method in which it is applicable 

 is to measure the blood-cells. The distinction of the 

 blood of any mammalian animal from that of the lower 

 classes of animals is easy, from .the fact that in mam- 

 malia only the cell is round and non-nucleated. The 

 distinction between the blood of man and that of the 

 lower mammalia turns entirely upon the micrometric 

 measurement of the cells. 



The following animals only have blood corpuscles 

 larger than man, i.e., exceeding -^-gW °f an mc ^ '■ t ^ ie 

 elephant, the great ant-eater, walrus, sloth, platypus, 

 whale,capibara, and (according to Wormley) the opossum. 

 Animals whose blood corpuscles are slightly below those 

 -of man in size, they having corpuscles from -j^Vo to -joVo" 

 of an inch in size, are the seal, beaver, musk-rat, porcu- 

 pine, monkey, kangaroo, wolf, and guinea-pig. None 

 of these are domestic animals. All other animals, 

 including all domestic species, have blood corpuscles of 

 a mean diameter less than -^Vo °f an inch, and, in fact, 

 those animals to which blood-stains found on the clothing 

 of criminals are commonly ascribed, such as the ox, pig, 

 horse, sheep, and goat, have corpuscles with a mean 

 diameter less than ^-5 of an inch. 



The question may, however, be raised whether the 

 blood corpuscules of all mammalian species have been 

 examined with sufficient care. It is very possible that 

 the animals here lumped together under the name 

 " monkey " may have blood-corpuscles not alike in size. 

 Especially is this the case with the anthropoid apes. 



Dr. Formad summarises the facts as at present known, 

 as follows : — 



1. The blood-corpuscles of birds, reptiles, and fishes, 

 being oval and nucleated, can never be mistaken for 

 human blood. 



2. Fresh human blood cannot be mistaken, under the 

 microscope, for the blood of any animal whose corpuscles 

 have a mean diameter of less than 4 u ' , or even ^Vc 

 of an inch. 



3. (a) If the average diameter of the corpuscles in 

 fresh blood be less than xiroo> tnen il cannot possibly be 

 human blood ; (b) if the diameter be above -g-g^jo inch, 

 then it may be human blood ; (c) if the blood corpus- 

 cules, after exhaustive measurement, give a mean 

 diameter exceeding ytitu °f an ' ncn > then it is human 

 blood, provided it is not the blood of any of the wild 

 beasts mentioned. 



These conclusions apply especially to fresh blood. 

 Dried blood, it is asserted, can be distinguished with 



equal accuracy, provided it has been dried rapidly. If 

 it has dried slowly it will have undergone decomposi- 

 tion, and its structure cannot be made out. A good 

 liquid for moistening dried blood is Virchow's solution, 

 consisting of thirty parts caustic potash and seventy 

 parts water. At least five hundred measurements 

 should be made in order to arrive at certainty as to the 

 average diameter of the cells. 



If the corpuscles have become spheroidal from the 

 absorption of moisture, or crenated from drying, they 

 may still be distinguished, because such changes are the 

 same in the corpuscules of all animals, and have their 

 proportionate and corresponding ratio of alteration in 

 form and decrease in size, the range or scale of decrease 

 being always alike in the same animal. 



The red blood corpuscules which have become 

 spherical by imbibing liquid have, according to Dr. 

 Formad's observations, the following mean diameters in 

 different species : man, 4 ~^ Q0 inch ; guinea pig 



d °g> thVo 

 sheep, - 



TTTo 



1 _ 

 TJ5T70 



inch ; rabbit, 49 ' u6 

 inch ; goat, -g^ 



inch ; wolf, ^S_o inch : 

 inch ; ox, ^^ inch ; 

 inch. 



These figures prove that the diameter of the corpus- 

 cles in each animal, when rendered artificially spherical 

 is about one-third less than that of the normal biconcave 

 or disc-like corpuscles of the same animal. 



Dr. Formad believes that human blood can thus be 

 positively distinguished from that of any other animal. 

 Other eminent microscopists do not feel equally satisfied. 



MICROSCOPIC MANIPULATION. 



THE remarks which follow are intended for workers 

 who have had some practice in the simplest modes 

 of preparing and mounting microscopic objects. They 

 form a sequel to the article " How to Work with the 

 Microscope," already published in the Scientific News, 

 (vol. i., N.S., p. 82). 



Let us suppose that some animal tissue is to be pre- 

 pared for microscopic examination. It is a good plan 

 to procure a small mammal, and remove from the fresh- 

 killed body a number of different tissues, say, stomach, 

 small intestine, a large nerve, such as the sciatic, and a 

 piece of spinal cord. These should be placed immedi- 

 ately in the hardening fluid. Only small pieces which 

 can be rapidly penetrated by the fluid should be taken. 

 No part of the object should be more than \ in. from 

 the surface. The fluid should be greatly in excess ol 

 what is required to cover the tissues ; thus four or five 

 small bits may be placed in about four ounces of fluid. 

 Trim the tissues to such shapes that by merely looking 

 at them you can see how they lay in the body and how 

 they must be cut. For instance, the long axis of the 

 piece may correspond to the long axis of the organ, 

 the narrow end of the piece to the narrow end of the 

 organ, and so on. 



Procure from the chemist 6 oz. of 10 per cent, solu- 

 tion of chromic acid, and keep it by you in a stock 

 bottle. Dilute some of this to \ per cent, for or- 

 dinary use as a hardening fluid. Various other solu- 

 tions possess special advantages of their own, but it is 

 of the first importance not to be bewildered by a 

 multiplicity of reagents, and the beginner will do well 

 to have only one process in his mind, until he has 

 thoroughly mastered it. The solution should be changed 

 after 24 hours, and then allowed to act for several 

 days (2 to 14, according to the size of the tissues). 



