ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 721 



established that the striation is due to the fact that in the act of contrac- 

 tion (when alone striation is observed) the fibre folds on itself, and so 

 gives rise to elevations alternating with depressions, which seen in 

 front appear as alternating dark and bright striae, and in profile as a 

 zigzag or sinuous curve. 



The cell-fibres, observed under polarized light, are, in the smooth 

 state, uniformly doubly refracting ; when contracted, on the other 

 hand, they exhibit, in the darkened field, an alternation of light and 

 dark bands, or if a purple tinted plate be introduced, an alternation of 

 purple bands with blue or yellow ones according to the orientation. 

 When a smooth fibre is accidentally greatly folded, the same alterna- 

 tion of isotropic and anisotropic bands is observable. 



The smooth fibres of the adductor muscle of the valves of acepha- 

 lous molluscs may, under the influence of purely artificial conditions, 

 acquire all the characters of striated fibres. Submitting the living 

 animal to the action of steam, the muscles are killed at about 45° to 

 50° ; their temperature continuing to rise, the smooth fibres at length 

 contract violently at one end of the adductor, and break away from the 

 shell. The smooth fibres at this end, dead and crisped by the heat, 

 acquire, in consequence of this purely physical action a striation so 

 fine and regular that it is in no way inferior to the delicate striation 

 of the fibrils of insects' wings, and presents the same appearances 

 as them in ordinary and polarized light. 



A fibre which has lost all contractility may therefore still 

 acquire all the peculiarities of structure and optical characters of 

 striated fibres, if fine and regular foldings have been produced. 



Blood Stains.* — Dr. C. 0. Curtman considers that after the 

 thorough investigation of the subject of blood-stains on linen or other 

 articles of apparel by Dr. J. J. Woodward no expert will be found to 

 assert that he can positively identify human blood by any microscopi- 

 cal device, particularly after having been dried and subjected to the 

 necessary preparation for microscopical investigation. Even if all 

 the difficulties in the way of such an identification were successfully 

 overcome, and the minutest distinctions could be made between the 

 different kinds of blood, such evidence would in many cases be ren- 

 dered absolutely nugatory by the doubts thrown upon the source of 

 the blood and its manner of transfer to the stained article by the 

 following facts : — 



Having been requested to make examinations of suspected blood- 

 stains, the thought occurred to the author that there was a possibility 

 of the transfer of human blood by predatory insects, such as the mos- 

 quito, bed-bug, &e. Experiments showed that the crushing of such 

 an insect will yield a stain of considerable size. Mosquitoes were 

 then captured and kept in close confinement after imbibing their fill 

 of human blood. At different periods they were crushed, and the 

 blood examined in various menstrua. In all cases, up to forty-eight 

 hours after a meal, a large proportion of human blood-corpuscles were 

 unchanged and readily recognizable. 



* Amer. Mon, Micr. Journ,, i. (1880) pp. 18i-6. 



