(4) True stomach, or proventriculus, furnishes gastric digestive juices that digest proteins and carbohydrates. (5) Gizzard is the grinding and mixing organ. (6) Pancreas furnishes digestive juices that digest fats, proteins, and carbohydrates, besides furnishing certain internal secretions. (7) Liver produces bile which helps digest food. [Illustration: _Figure 40. Loft cleaning equipment._ TL70209] (8) Intestines provide space for food while it is being digested and absorbed by the blood stream. The intestines also furnish some digestive juices. _c._ CIRCULATORY SYSTEM. The circulatory system consists of the heart, arteries, veins, and capillaries. Its function is to convey nourishing blood from the heart to all parts of the body and to dispose of the waste material produced by the working tissues. The heart consists of four chambers: two ventricles and two auricles. The right auricle receives the stale blood from the veins and pumps it into the right ventricle which pumps it through an artery to the lungs. Here waste matter, such as carbon dioxide, is eliminated from the blood and fresh oxygen is restored. The blood then returns to the heart through a vein entering the left auricle. Proceeding from the left auricle to the left ventricle, it is pumped out through the arteries to the capillaries, which are the smallest vessels of the body. The capillaries circulate the blood through every tissue of the body, dispensing oxygen and food. The blood then picks up waste material on its return to the heart through the veins. The circulation of blood in the pigeon is very rapid, and with the heart beating 200 to 300 times a minute, only a few minutes are required to complete the circuit. _d._ REPRODUCTIVE SYSTEM. (1) Male birds have two testes (testicles). (2) Female birds have one (left) ovary and one oviduct, or egg tube, through which the yolks pass to get the albumin, shell membrane, and shell. _e._ URINARY SYSTEM. The kidneys take impurities out of the blood, and pass them into the cloaca (combination bladder and rectum). 51. Indications of Sickness _a._ The common indications of sickness are— (1) Refusing to eat. (2) Dull, watery eyes. (3) Droopy appearance with ruffled feathers and no desire to move. (4) Green, watery droppings. If such droppings are noted in the loft all birds should be watched until the sick one is detected. _b._ The easiest and best way to detect sick pigeons is to observe the birds at feeding time. The pigeoneer should also examine all birds as they are being basketed for training tosses. 52. Diseases Pigeons are subject to numerous infectious and contagious diseases. These diseases are caused by germs such as bacteria and viruses, and are transmitted in poor feed, dirty water, unclean lofts, and similar conditions showing mismanagement. Infectious diseases are contagious if the birds themselves transmit germs to one another.