the Latin dissertation Pander warmly referred to DOllinger's 

 kind treatment and to the readiness with which he gave him 

 assistance, and also referred to the friendly conditions and 

 group discussions in the laboratory. 



In the introduction, Pander described his method of investi 

 gation. First, he cited the necessity of having available 

 extensive material, since earlier disagreements about chick 

 development originated from the fact that the disputants 

 could not investigate controversial data because of a lack 

 of material. In order to obtain a sufficient number (up to 

 forty) of embryos at one stage, Pander rejected the use of 

 brood hens and instead used an incubating machine of Colman's 

 system, about which Blumenbach had spoken favorably. Pander 

 objected to the current prejudice against incubators, referring 

 to the fact that egg development occurs normally in them and 

 that chickens, as usual, hatch out on the twenty-first day. 

 According to Pander, the temperature in the incubator should 

 not be lower than 28° nor higher than 32°C. A total of more 

 than two thousand developing chicken eggs were used. 



The least understood period of chick development was 

 considered to be the earliest. For this reason, Pander 

 limited his investigations to the first five days of incuba- 

 tion. "In this period," Pander wrote, "when the basics of 

 all parts were laid, we did not find anything special that 

 deserves mentioning. "12 Opening the egg, Pander said, should 

 be done in water. To study the early stages (up to the fifth 

 day) , it is necessary to watch for complete separation of the 

 blastoderm from the surrounding parts, because there the 

 processes of embryonic formation actually take place. With 

 this objective, around the cicatrice or, at later stages, 

 along the terminal sinus, Pander cut a segment of the yolk 

 membrane, after which the egg submerged in water separates 

 by itself from the blastoderm. Soon after that, Pander con- 

 tinued, we must begin observing with different types of 

 complex and simple microscopes, with greater or smaller 

 magnification. He recommended placing the observed object 

 on a dark background; then it is comfortable to use the 

 glasses which cover pocket watches. To prepare the blasto- 

 derm with instruments, Pander used saucers covered with a 

 layer of wax. 



12. Pander, DISSERTATIO, p. 12. 



243 



