Composite Chicks

The day of men made from bits and pieces may be distant, but it is already possible to replace the head of an embryonic chicken. Last week Yale University told how Mira Pavlovic, 28, a visiting research associate from Yugoslavia, performs the graft, operating on eggs that have been incubated for 33 to 40 hours. At this point the embryo is 0.2 in. long, and the blood system is so primitive that the organism does not bleed.

Following a technique originally developed by another Yugoslav, Petar N. Martinovitch, she cuts a small square hole in the eggshell. Then she uses modified watchmaker's forceps to cut off two of the five parts of the undeveloped brain. The detached tissue is picked up with a suction pipette and transplanted to the head of another embryo that has been prepared by similar surgery to receive it. Finally, the hole in the second eggshell is covered with transparent material, and the egg with its patchwork embryo is replaced in the incubator.

Researcher Pavlovic has developed such skill that out of a recent series of 100 grafted embryos 30 did not die until their last day of incubation, and six hatched into living chicks. One of these lived 55 days, another 70 days. They grew more slowly than normal chicks and appear to have died because their composite brains did not properly control their digestive apparatus.

Their composite heads and brains seemed normal. The host chicks were Rhode Island Reds but the grafted tissue came from a black breed and it showed its origin by the growth of black feathers on the top of the head. The upper beak, eyes, ears, forebrain and half of the midbrain were grafted too, but the chicks could see and hear well and seemed to be normally alert. The one that lived 70 days learned to respond to a whistle, which many birds never learn.

Professor John Nicholas, under whom Researcher Pavlovic is working, thinks the experiment shows that young embryonic tissue from different individuals does not yet have the incompatibility that prevents the grafting of adult tissues. He hopes that it will soon be possible to advance from chicks to mammals. Already his laboratory has transplanted parts of the brains of rat embryos to unhatched chicks. Some of them survived and grew for 17 days, but none so far have hatched into live chicks with rats' brains.

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