1880.] 



MICROSCOPICAL JOUR]NAL. 



185 



troscope, that instrument has also 

 been held by many to be an un- 

 erring detective of blood. 



But by degrees the illusion in re- 

 gard to the positive and unassail- 

 able results of the microscope has 

 vanished, and at present, (especially 

 since the thorough investigation of 

 the subject by Dr. J. J. Woodward, 

 U. S. A.) no expert would be found 

 bold enough to assert, in the face of 

 contrary evidence, that he can posi- 

 tively identify human blood by any 

 microscopical device. The blood 

 discs of the dog, especially, are so 

 nearly of the size and shape of hu- 

 man blood, that no means, at present 

 known, will discriminate wdth abso- 

 lute certainty between the two, even 

 in the fresh state, much less after 

 having been dried and subjected to 

 the methods of preparation neces- 

 sary for microscopical investigation. 

 The spectroscope does, with great 

 accuracy, reveal the presence of 

 blood, by the absorption bands 

 characteristic of the hemoglobin, but 

 cannot make any distinction between 

 the various blood-corpuscles aiford- 

 ing the coloring matter. 



But even were all of those diffi- 

 culties successfully overcome, and 

 could the minutest distinctions be 

 made between the different kinds 

 of blood, such evidence would, in 

 many cases, be rendered absolutely 

 nugatory by the doubts thrown upon 

 the source of the blood and its man- 

 ner of transfer to the stained article 

 by the following facts : 



Having been applied to, last Win- 

 ter, to make examinations of sus- 

 j)ected blood-stains, the thought 

 occurred to me that there is a pos- 

 sibility of the transfer of human 

 blood by means of predatory insects, 

 such as the mosquito, the bed-bug 

 and similar others. Experiments 

 showed that the crushing of such 

 an insect, loaded with its meal of 

 human blood, will yield a stain of 



considerable size, much larger than 

 I had anticipated. I then captured 

 some mosquitoes, after they had im- 

 bibed their fill of blood, and kept 

 them alive in close confinement. 

 They were then, after different pe- 

 riods of time, crushed and the blood 

 examined, mixed with various men- 

 strua for dilution. In all cases up 

 to forty-eight hours I found a large 

 proportion of the red corpuscles of 

 human blood still unchanged, and 

 quite readily recognizable. I next 

 examined the blood of the mosquito, 

 which had not been permitted to 

 feast on the human subject. The 

 size and color of these corpuscles of 

 mosquito blood are so different from 

 human, that no mistake can pos- 

 sibly arise from this source. 



In the last few weeks Dr. E. 

 EvQrs was kind enough to assist 

 me in a considerable number of 

 micrometric determinations of the 

 human blood taken from the mos- 

 quito, after various intervals, and 

 tlie corpuscles of mosquito blood 

 proper. The task has been a la- 

 borious one, owing to various diffi- 

 culties, not the least among which 

 was the selection of a proper men- 

 struum for dilution. Glycerin in 

 various dilutions, gave excellent 

 definitions of the human blood-cor- 

 puscle, but left the margins of that 

 of the mosquito so ill-defined as to 

 make accurate measurements very 

 difficult. After various trials, we 

 found alcohol of about 80 per cent, 

 the l)est medium for examining 

 mosquito blood, and very fair for 

 the human blood-corpuscle, al- 

 thouo-h both shrink somewhat in 

 the alcohol. 



Our results'" are as follows : — 

 Human blood (after imbibition 

 by the mosquito) averages (red cor- 

 puscle,) in dilute glycerin, Y.4 

 micro-millimetres (or -g-gVir i^cli) ; 



* These results are the average of more 

 than one hundred careful measurements. 



