K EXPERIMENTAL MAMMALIAN EMBRYOLOGY 



Suggested Procedures for Obtaining and 

 Experimenting with the Mouse Embryo 



PURPOSE: To introduce the student to a mammalian embryo which can be used easily in 

 laboratory xperimentation. 



MATERIALS: The mouse . Any strain or species of mouse which is adjusted to laboratory 

 conditions may be used. Some are more viable than others, some more fertile 

 (larger and more frequent litters), and some have low levels of intra-uterine death, 

 resorption and anomaly development. A white Swiss strain is, in general, very sat- 

 isfactory. * 



Cage : There are various types from wood, to plastic, to stainless steel. Sat- 

 isfactory size is 7 X 10 x 6. 5 inches, with removable cover and built-in food 

 hopper and holder for water bottle. There should be a holder for the record 

 card, with 1/2 inch lip. The capacity of such a box is 5 to 7 adult mice, or 

 two litters for the first two weeks. (See illustration) 

 Food : Various rat, dog, and mouse chows can be used, supplemented when there 

 are litters with coarse oatmeal. These foods are generally well balanced, 

 with vitamins, etc. added. 

 Water : This must be continuously available from an inverted bottle having a 

 glass or stainless steel tube from which the water will not run by itself. 

 The outlet should be checked because the lack of water can cause anorexia 

 and death. 

 Temperature : Should be near 72 F. , but tolerance is wide. 



Antiseptics and diseases: Rodents are susceptible to certain diseases which may 

 ruin a research project. However, caution as to source of animals, brief 

 quarantine, and prophyllaxis should be adequate to keep epidemics under 

 control. For ringworm use iodine or mer curochrome painted on, or specific 

 powder; for mites, bedbugs, lice, etc. , any powder insecticide that is non- 

 toxic to mammals, or brief dipping in 1% carbolic acid; for mouse typhoid 

 (showing diarrhea, anorexia, death) there is no known cure, but it can prob- 

 ably be prevented by adding 1% tetracyclene or terramycin to the drinking 

 water for a two-week period, and occasionally thereafter. Food treated by 

 soaking in an antibiotic, and drying in forced draft, is good for newborn and 

 weanling rodents. There are vaccines which may prevent the disease. Ring- 

 worm is almost universally prevalent but rather innocuous. 



METHOD: The mamnial (except primates) will mate only when mature eggs are available 

 and could be fertilized. That is, the female will not accept the male except at estrous. 

 The mouse has a 5 to 5. 5 day estrous cycle and estrous seems to occur most fre- 

 quently at night (see papers by Austin and by Braden). A laborious but fruitful pro- 

 cedure is to examine mice by the vaginal smear method, segregating those in estrus 

 or pro-estrus for immediate mating. Matings may be observed to get exact timing of 

 conception but it is possible to estimate this time within a few hours, as follows: 



1. Place sexually mature male with 5 or 6 mature females at 5 P. M. (Mice 

 should be 3 or more months of age). 



2. Remove male at 9 A. M. the next morning. 



3. Examine each female for the presence of a vaginal plug. This consists of 

 secretions from the vesicular and coagulating glands of the male and appears 

 as a white coagulum blocking the vaginal orifice. (See illustration) A double 



♦ Mice can be obtained from Carworth Farms, New |City, N.Y. , Roscoe B. Jackson Memorial Laboratory, Bar Harbor, Maine. 

 (Normal and tumor-bearing strains) and Texas Inbred Mice Company, R. F. D. #7, Box 1232-C, Houston 21, Texas. 



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