Journal of Applied Microscopy. 



101 



small vessel and thoroughly stir with 

 a sufficient quantity of the mounting 

 fluid to form a stiff cream. Transfer a 

 drop of the mixture to the glass slide 

 and dilute with a small drop of the 

 mounting fluid before applying the 

 cover glass. 



The microscope used should place at 

 the operator's disposal powers varying 

 from 325 to 450 diameters, and should 

 be provided with a polarizing apparatus. 

 An_ eyepiece micrometer is also of value, 

 especially so if rice and other starches 

 having polyhedral grains are to be 

 looked for. 



While textbook illustrations and 

 descriptions are of value, they should 

 not be relied upon for a knowledge of the 

 characteristics of starches. A careful 

 study of pure materials likely to be 

 found in the mixtures to be examined 

 cannot be neglected with safety in any 

 microscopical examination. 



While the grains of wheat starch do 

 not usually show the characteristic 

 cross under the influence of polarized 

 light with marked distinctness, almost 

 every sample of pure wheat flour will 

 be found to contain an occasional grain 

 of starch that will show as bright a 

 cross as do the average maize starch 

 grains. By careful examination, how- 

 ever, it can usually be noted that the 

 angles between the arms of the cross 

 seen on grains of wheat starch are 

 decidedly different from those seen on 

 grains of corn starch. The microscopic 

 appearance of the starch grains of the 

 common cereals is found in part nine, 

 bulletin thirteen of this division, now 

 passing through the press. 



Laboratory of the Division of Chemis- 

 try, U. S. Department of Agriculture, 

 Washington, D. C, May 24, 1898. 



A Simple and Convenient Method 

 for Demonstrating the Circula- 

 tion of the Blood in the Capil- 

 laries. 



For several years the writer has used 

 tadpoles to demonstrate capillary circu- 

 lation, both in thq external gills (which 

 are absorbed ten days or two weeks 

 after hatching) and in the transparent 

 tissue of the tail. These show the 

 branching of the arterioles remarkably 

 well; and the systole and diastole of the 

 heart are plainly noticeable in the alter- 

 nating increase and diminution in the 

 rate of flow of blood in the capillaries — 

 especially in those of the g'ills. In the 

 latter, the blood goes up on one side of 

 the gill and down on the othei', in jerks 

 like the cups in a chain-pump moving 

 by jerks. 



Tadpoles are more readily accessible 

 than frogs, smaller and more easily 

 manipulated, and their tissues thinner 

 and more transparent than is the web 

 of the frog's foot, so often used for 

 this purpose. Until this spring I had 

 difficulty in keeping them still enough 

 to demonstrate the circulation to fresh- 

 man and sophomore students who have 

 had little experience in the manipulation 

 of the compound microscope; but an 

 accidental discovery obviated this diffi- 

 culty, and I give it now in the hope 

 that it may be of assistance to teachers 

 and to others who may have to work 

 under similar difficulties. 



I spoke to a friend of this difficulty of 

 keeping the tadpoles still, and he sug- 

 gested that I try pinning them down. 

 This I proceeded to do, and flrst thought 

 of pinning the specimen on paraffin and 

 examining with the top light, but my 

 eye chanced to fall upon some thin, 

 transparent sheets of celloidin which I 

 had bought for embedding purposes, and 

 I concluded to try this. I pinned one 

 specimen to celloidin, but the experi- 

 ment failed, either because the sticking 

 stopped the circulation or because I did 

 not take time to focus properly, as I was 

 in a hurry. 



I next placed a moist tadpole on the 

 celloidin without pinning and without 

 using a cover glass. The experiment 

 was a perfect success. The water soft- 

 ened the celloidin and made it sticky, 

 so that the tadpole's tail became glued 

 hard and fast. By adding a drop of 

 water from time to time, I used the 

 same specimen to demonstrate capil- 

 lary circulation to two consecutive sec- 

 tions of my zoology class. Mount moist, 

 not using too much water, and examine 

 with a two-thirds inch objective. 



Celloidin may be purchased of any 

 dealer in microscope supplies, but that 

 sold by Schering and Glatz of New York 

 is said to be the best for embedding 

 purposes. 



T. O. Mabry, M. a., M. S. 



Dept. of Natural History and Geol- 

 ogy, University of Mississippi, May 24, 

 1898. 



PLEASE FILL OUT THE BLANK 

 ON PAGE VIL 



Duplicate blanks with return 

 postage will be mailed on request, 

 as we intend to make the Direc- 

 tory as complete as possible. Send 

 the names of all interested in the 

 microscope. 



