HETEROGENETIC—A UTOGENETIC 



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Heterogenetie. 



These are external or adventitious, and may be divided into: — 

 I. Those belonging to the glass slide. 

 II. Those belonging to cleaning or drying materials. 



III. Those coming via the air. 



IV. Those coming from the skin. 



V. Those coming from the intestines. 



The Glass Slide. — Everyone is well aware of the peculiar marks 

 which may appear on old glass slides, and which retain the stain, 

 thus giving rise to pseudo-trypanosomes, yeasts, and many other 

 forms. 



Perhaps the most interesting of these are the ' X bodies ' 

 (Horrocks and Howell) which appear in Romanowsky films as 

 roundish bodies, with a small blue circular centre surrounded by 

 four or more faint concentrically arranged capsules, and which 

 Chamberlain and Vedder have shown to be artefacts present in the 

 glass slide. 



Cleaning and Drying Materials. — Cotton fibres may be introduced 

 from a cloth in cleaning slides. Blotting-paper, if used twice for 

 drying blood slides, may introduce one kind of blood into another 

 or bacteria into a blood film. 



The Air. — Insect scales, plant hairs, animal hairs, yeasts, and 

 pollen grains, may all be introduced into blood films from the air, 

 and especially multiseptate fungal spores. 



The Skin. — Pieces of dirt, epithelial scales, and bacteria, may come 

 from the skin. 



The Intestine. — In obtaining films during a post-mortem or from 

 an animal which has been shot there is danger of contamination of 

 the blood with spirochaetes and other organisms from the intestine. 



Autogenetic. 



These are bodies which are really in the blood, whether natural 

 products or artificial productions. 



Fresh Blood— Erythrocyte. — -In anaemic blood the erythrocytes 

 become deformed, forming oval, pear-shaped, tailed, or irregular 

 bodies called poikilocytes, allied to which are the pecuHar chain-like, 

 droplet-like, and filament-like bodies figured by Nuttall and Balfour 

 as produced when taking films in high air temperatures. Some of 

 them may be mistaken for parasites, but only by beginners. 



A crenation seen in a deformed or in an ordinary corpuscle may 

 in certain focal planes look like a malarial parasite. 



Vacuoles have clear-cut margins, do not move, do not possess 

 pigment, and are quite clear, yet they give rise to trouble, and may 

 be mistaken for piroplasma or for malarial parasites. 



The glassy body mentioned above, when easily visible, is often 

 mistaken for a parasite, and is probably the explanation of the 

 ' maraglianos ' or dehsemoglobinized spots which have been de- 



