/K EXPERIMENTAL CHICK EMBRYOLOGy 



No attempt will be made here to describe the most delicate of the transplantation opera- 

 tions (e. g. , those by Willier and by Hamburger and their students) that have been per- 

 formed on the chick embryo. The student is, however, directed to the work of these 

 investigators, particularly to inter-specific transplantations. 



Recent work of Spratt (1947, 1948) has demonstrated that the extreme precautions of a 

 dust-free operating room, ultra-violet lighting, masking, etc. , are not necessary so 

 long as reasonable precautions are taken to avoid the actual introduction of bacteria into 

 the hen's egg. It is therefore safe to predict that the chick embryo will be used increas- 

 ingly in courses in Experimental Embryology, and that it will supplement the work on 

 the amphibia admirably well. The hen's egg is available during the months when am- 

 phibian material is scarce. 



Aside from the general procedures for handling the hen's egg in the laboratory, the ex- 

 perimental procedures to be described will include (1) Determination of morphogenetic 

 movements by means of vital dyes and charcoal particles, (2) Explantations or the cul- 

 turing of isolates on artificial media (3) Chorio-allantoic grafting and (4) Transplanta- 

 tions. 



This exercise has the single experimental object, the hen's egg. It involves four differ- 

 ent procedures and in this respect this exercise cannot be weighed with the others of this 

 Manual. It is recommended that the material on the hen's egg be assigned to the second 

 half of the second (Spring) semester, when the amphibian material is no longer available 

 and after the student has had the benefit of some months of experimental and operational 

 experience with amphibian material. 



49. PROCURING AND CARE 

 OF LIVING MATERIAL 



Procuring of eggs: One must establish a reliable source of highly fertile eggs, which 

 prove to be perfectly normal in development. There are the usual seasonal variations in 

 fertility with the low point during late Summer and Fall, and the high point just after the 

 peak of the Winter. With optimum conditions fertility may reach as high as 90% but the 

 low point may go to Z5% or even less. There is no evidence that any particular breed 

 lends itself better than others to operational procedures. However, certain flocks of 

 hens give more viable eggs, particularly when they are provided with adequate sunlight. 



Storing of eggs: If possible, eggs should be used shortly after being layed. However, 

 eggs may be stored at cool temperatures (10°C. ) for as long as a week. The percentage 

 of development will drop rapidly thereafter. 



Incubators : The small (Oakes) incubators will hold several dozen eggs and are quite sat- 

 isfactory although they are not provided with as sensitive temperature and humidity con- 

 trols, and forced-air draft for ventilation, as are other and larger models. The large 

 (Buffalo) incubators are excellent for the incubation of larger numbers of eggs, and the 

 physical factors are well controlled. Place the incubator away from drafts and sunlight. 



Temperature control : Most incubators are provided with temperature control devices 

 regulated close to the optimum range of 102° - 103° F. (about 38. 2-39. 0° C. ). If the 



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