Santa Claus, the tooth fairy, an honest lawyer and an old drunk are walking down the street together when they simultaneously spot a hundred dollar bill. Naturally, the American Bar Association was outraged, and filed suit, but the NIH presented some very good reasons for the switch. The lab assistants were becoming very attached to their little rats. This emotional involvement was interfering with the research being conducted. No such attachment could form for a lawyer.
Lawyers breed faster.
Lawyers are much cheaper to care for and the humanitarian societies won't jump all over you no matter what you're studying. There are some things even a rat won't do. However, sometimes it very hard to extrapolate our test results to human beings. A certain lawyer was quite wealthy and had a summer house in the country, to which he retreated for several weeks of the year. On one particular occasion, he invited a Czechoslovakian friend to stay with him.