SECTIONAL TRANSACTIONS.—D. 321 
environment in which the different types have been developed. Maize has 
developed the lard type in Hungary and America; skim milk and cereals 
the bacon type in Denmark ; and skim milk and meat meal the pork type 
in New Zealand. 
Conclusions —Since the genetic characters concerned are so dependent 
for their expression on nutrition, and are mostly of a ‘ developmental ’ char- 
acter, the best means of directive improvement is selection (by progeny 
tests) in an environment which stimulates the development of the character 
in question. The further development of these commercial qualities in 
our animal depends, like ‘ civilisation qualities ’ in man, on the creation of 
a better environment for the development of the characters concerned. 
Mr. A. D. BucHanan SmitH.—Milk. 
It is presumed that the purpose of this discussion is to determine whether 
the science of genetics can offer reasonable help to the livestock producer. 
If so, then by what means ? 
Genetical experiment in respect of milk is easier than in the case of meat, 
since the former is more amenable to measurement, both of quantity and 
quality. As regards milk, there are two main difficulties. The first is to 
discriminate between those factors which affect the productivity of the 
animal and are not of genetic origin. ‘The difficulty of doing so is one of 
the rocks upon which many experiments have foundered. To overcome 
this, the method now being adopted in the United States and at Edinburgh 
is to maintain a herd of dairy cattle under a uniform system of management 
over as long a period of years as possible. Thus, although the production 
of one generation takes place years after the production of the ancestral 
generation with which it is to be compared, the comparison may be 
considered to be reasonably straightforward. 
Actually the science is not so much concerned with the determination of 
the number of genetic factors involved, but rather with an analysis of the 
lactation curve of individual animals under standard environment. (Animals 
giving similar yields may do so in spite of different genetic constitutions.) 
It is of fundamental importance to understand the action and reaction with 
each other of the various characters and components of milk. Deliberate 
research of this nature will discover whether abnormal modes of inheritance 
are operating, such as sex linkage and combinations of genes which act as 
inhibitors of yield. The possibility that economic production may actually 
be best obtained when genes are in a heterozygous state is discussed, as 
also whether certain combinations of characters, desirable from the stand- 
point of the practical breeder, are genetically possible. 
The principal difficulty of the disentanglement of genetic factors can now 
be overcome by means of the experimental herd with controlled environ- 
ment. This leads to the next difficulty, that the analysis may reveal so 
many genetic factors interacting with each other as to make the synthesis of 
the problem almost an impossibility as regards practical application. 
Simple selection is discussed, and the work of Winter with maize is 
quoted, as well as the observations of ‘ Student’ and Fisher. Owing to 
the immense amount of time involved, a similar improvement in productivity 
cannot be expected in our dairy cattle. Selection has great value on 
unimproved stock, but as the quality rises, the rate of improvement 
decreases rapidly. The ‘ progeny test’ is discussed as the logical refine- 
ment of existing methods of selection. The conclusion is drawn that 
without fundamental knowledge the rate of improvement is bound to 
get slower. 
