TRANSACTIONS OP SUB-SECTION K. 607 



coat-colour may help to throw light on the more complicated question of the 

 breeding of a classic winner. 



Homozygous Hunters. 



It is generally admitted that the most useful type of light horse is the 

 hunter. Recently Professor Cossar Ewart and myself have drawn up a scheme 

 of experiments in horse-breeding for the use of the Board of Agriculture, the 

 object being to make a line of homozygous hunters. At present there is no such 

 thing as a pure-breeding hunter; our studies have been mainly based on the 

 thoroughbred 'chaser as probably the most suitable material upon which to work. 



Our investigation of the Stud-Book and Racing Calendar to find suitable 

 animals with which to experiment has led us to the discovery of the exist- 

 ence of homozygous 'chasers, though in very few numbers. After eliminating 

 many hundreds of heterozygous and doubtful animals, we have found five mares 

 and three stallions, which, when bred together, have given nothing but horses 

 of the 'chase'' type, as tested on the racecourse and at the stud. 



In view of this fortunate find of what might perhaps be called a 'chaser ' pure 

 line,' we have recommended the Board of Agriculture to purchase some of the 

 offspring of these animals in order to increase the ' pure line,' and we hope that 

 this experiment will help us to solve the problem of the making of a homozygous 

 hunter. 



2. Aboriginal Races and little-known Breeds of Domestic Sheep. 

 By H. J. Elwes, F.R.S. 



3. The Inheritance of Milk-yield in Cattle. By Professor James Wilson. 



Before any theory as to the inheritance of milk-yield can be formed, it is 

 necessary to find how yields can be reduced to the normal, because individual 

 yields are frequently abnormal. A normal yield may be taken as that in which 

 the next calf is born about twelve months after the previous one. Apart from 

 illness (and cases in which it occurs must be eliminated), the chief causes of 

 abnormality are : — 



(i) Time of calving, 

 (ii) Food and shelter, 

 (iii) A prolonged lactation, 

 (iv) A shortened lactation, 

 (v) The cow's age. 



When these causes of abnormality have been allowed for, it is found that full- 

 sized cows fall into three grades, viz., cows that give approximately from 500 to 

 600 gallons of milk a year when of mature age, cows that give from 650*to 850. 

 and cows that give about 1,000. The two extreme grades are approximately 

 'pure,' while the middle grade is an intermediate hybrid between the extremes. 



4. Commercial Ovariotomy in Pigs. By F. H. A. Marshall and 

 K. J. J. Mackenzie. 



5. Temperature Variations during the Oestrous Cycle in Cows. 

 By F. H. A. Marshall and, K. J. J. Mackenzie. 



6. The Fixation of Nitrogen by Free-living Soil Bacteria. 

 By Professor W. B. Bottomley, M.A. 



In a paper read before the Sub-Section last year under the above title, experi- 

 ments were described showing that the bacteria Azotobacter and Pseudomonas 

 fix more nitrogen per unit of carbohydrate when grown together than when 

 grown separately. The results were criticised somewhat adversely because it 



