4. SPECIES DIFFERENCES IN BILE SALTS
225
have been shown to be probably microbial artifacts. This disposes of the
view, at one time held, that the keto acids are intermediates in bile salt
formation and possibly of reasons for thinking that 3a-hydroxy-7-oxocholanic acid (formerly called nutriacholic acid) is a character specific
to the coypu, or that ursodeoxycholic acid is characteristic of bear's bile.
It has, however, been suggested (92a) that 3a-hydroxy-7-oxocholanic
acid in guinea pigs is formed "without action of enteric microorganisms."
The status of 3o:,7/3,12a-trihydroxycholanic acid is uncertain, as is
that of allocholic (Ohta's) acid. The distribution of 23-hydroxylated
C 24 acids (phocaecholic, etc.) suggests that 23-hydroxylation is a true
species character.
No work has been reported on the possible effect of intestinal
microorganisms on any bile salts other than those containing C 24 acids.
D. USE OF THE CHEMICAL NATURE OF BILE SALTS
AS A SPECIES CHARACTER
If the qualifications mentioned above are borne in mind, it seems
possible that consideration of the chemical nature of bile salts may prove
useful in biological studies. In cases in which morphology is an uncertain guide the chemical evidence may be found valuable. It has
been cited recently (94) in a comparison between the West African
cutting-grass (cane rat) Thryonomys swinderianus and the South
American coypu Myocastor coypus. These rodents are so closely similar
that at one time Simpson (120) placed them both in the superfamily
Octodontoidea. However, Wood (121) and others disputed this, on
paleogeographical grounds. An examination of the bile salts showed
that Thryonomys conjugated only with taurine, whereas Myocastor, like
the guinea pig, had mainly glycine conjugates. It was felt that this
evidence supported Wood's rather than Simpson's (1945) views. Similar
comparisons might well be made in other instances in which systematists
disagree about morphological evidence.
Light may possibly be thrown on evolutionary history by bile salt
examinations. For example, if a lizard could be found which hydroxylated deoxycholic acid as do the Boidae (see above), there might be an
a priori case for considering it as a limbed ancestor to these snakes.
Again, a study of the occurrence of cholic acid and of 6a-hydroxylated
bile acids among the Suidae might help in unraveling the history and
relationships of this family. Many similar examples will occur to
biologists, and help might reasonably be expected in those cases where
the bile salts show unusual or rare features. It seems obvious, however,
that in many, perhaps most, "modern" species the bile salts are generalized and do not show qualitative chemical features which appear
225
have been shown to be probably microbial artifacts. This disposes of the
view, at one time held, that the keto acids are intermediates in bile salt
formation and possibly of reasons for thinking that 3a-hydroxy-7-oxocholanic acid (formerly called nutriacholic acid) is a character specific
to the coypu, or that ursodeoxycholic acid is characteristic of bear's bile.
It has, however, been suggested (92a) that 3a-hydroxy-7-oxocholanic
acid in guinea pigs is formed "without action of enteric microorganisms."
The status of 3o:,7/3,12a-trihydroxycholanic acid is uncertain, as is
that of allocholic (Ohta's) acid. The distribution of 23-hydroxylated
C 24 acids (phocaecholic, etc.) suggests that 23-hydroxylation is a true
species character.
No work has been reported on the possible effect of intestinal
microorganisms on any bile salts other than those containing C 24 acids.
D. USE OF THE CHEMICAL NATURE OF BILE SALTS
AS A SPECIES CHARACTER
If the qualifications mentioned above are borne in mind, it seems
possible that consideration of the chemical nature of bile salts may prove
useful in biological studies. In cases in which morphology is an uncertain guide the chemical evidence may be found valuable. It has
been cited recently (94) in a comparison between the West African
cutting-grass (cane rat) Thryonomys swinderianus and the South
American coypu Myocastor coypus. These rodents are so closely similar
that at one time Simpson (120) placed them both in the superfamily
Octodontoidea. However, Wood (121) and others disputed this, on
paleogeographical grounds. An examination of the bile salts showed
that Thryonomys conjugated only with taurine, whereas Myocastor, like
the guinea pig, had mainly glycine conjugates. It was felt that this
evidence supported Wood's rather than Simpson's (1945) views. Similar
comparisons might well be made in other instances in which systematists
disagree about morphological evidence.
Light may possibly be thrown on evolutionary history by bile salt
examinations. For example, if a lizard could be found which hydroxylated deoxycholic acid as do the Boidae (see above), there might be an
a priori case for considering it as a limbed ancestor to these snakes.
Again, a study of the occurrence of cholic acid and of 6a-hydroxylated
bile acids among the Suidae might help in unraveling the history and
relationships of this family. Many similar examples will occur to
biologists, and help might reasonably be expected in those cases where
the bile salts show unusual or rare features. It seems obvious, however,
that in many, perhaps most, "modern" species the bile salts are generalized and do not show qualitative chemical features which appear