Blood - one of the 5 types of Jutsu

[Ichike]

In Naruto, there were 5 types of Jutsu, not 3:

Taijutsu
Ninjutsu
Genjutsu
Blood
Ninja Tool

Blood basically was summoning. From what we can tell, it involved signing a contract with an animal (although Ten Ten manages to summon weapons all of the time), and then the level of their skill in that area (and the higher their chakra) depends on how big an animal they can summon, and what they do.

Then, depending on your level in blood, and how much chakra you choose to pump in to the summoning depends on what you get for them.

Of course, all of these summons require a rather complex ritual to bind yourself to the animal, and then each time you need to use blood, which means that while they are summoned you lose health (1 hp per attack round) until they disappear. Summons have a limited life span however, which could be determined based on their level. Top level summons should last perhaps half a day game time at most. They can all of course be dismissed, and if they die then they disappear.

Examples:

Hound:
(this was Kakashi's summoning animal)
Tracking animals, which let you find out the exact directions to anything anywhere in the entire MUD. At later levels it lets him summon higher level animals, then even 7 at a time. None of them, however, are particularly good at fighting.

Toad:
Some of them give advice, while others fight for you. The highest level one, the Chief Toad, is massive and can seriously hurt. But some high level ones give bonuses to your skills too. Costs enormous amounts of chakra to use, however, and low amounts of chakra mean just toads that do stuff all.

Serpent:
(this was Orochimaru and his ex-student Anko's summoning animal)
Low level ones were hidden snake hands, to attack with pure damage. Higher level ones mean larger and larger snakes, including the ones that attacked Naruto in the Forest of Death, who have the chance to swallow an opponent. However, with snakes there is the chance that on summoning they will turn wild and attack the person who summons them. To appease them, they must be given sacrifices. So you must have killed a certain amount of people before you can summon each level snake. Whilst killing, you don't get Ryo for corpses anymore, because that goes to the Snake.

Leech:
Can heal people, cure broken ribs/arms and cure poison, and when summoned if it doesn't get killed, then it will slowly remove all of your damage. Unfortunately, they get killed easily and any enemies will try to kill your leech, so you have to protect them. Higher level leeches have more hps and can take more damage. Highest level leeches can even attack to a limit degree. Mostly a defensive type summon.

Weapons:
(Ten Ten style)
Lets you summon weapons to hurt someone for massive amounts of damage in a single hit. The higher the level summon, the more weapons you get and the harder you hit.

[Hitoshi]

Well, summoning wasn't a specific jutsu type. Summoning is a ninjutsu (Kuchiyose no Jutsu)

[Ichike]

Summoning uses blood.

If you look at the Ninja cards (referred to as Bingo cards I think), in use during the Chuunin exam final battles, and later on when getting missions, they refer to 5 elements, one of which is blood.

All ninjas get summoning, but they only get one animal/type each.

Mind you, there are some characters that don't seem to have any summoning. I can go over them:

Kakashe - Hound
Naruto - Toad
Sasuke - Serpent?
Sakura - Leech?
Tsunade - Leech
Jiraiya - Toad
Shino - (none) (but he has bugs inside him)
Kiba - (none) (but he has a pet dog)
Hinata - (none)
Neji - (none)
Tenten - Weapons
Rock Lee - (none)
Chouji - (none)
Shikamaru - Butterfly? (seemed to be used when looking at Chouji)
Ino - Leech?
Shizume - Leech
Anko - Serpent
Gai - ??? - Hound?
The third hokage - Monkey
Orochimaru - Serpent
Asuma - ???
Kurenai - ???
One of the sound ninja 4 - Spider
Fourth hokage (in flash backs) - Toad
(Sand ninjas during big assault) - Serpent

Of course, those without summoning might get it later on. Medical Ninjas all seem to have Leech.

Perhaps I am wrong that that is what blood meant. However, they all use blood. And calling them Ninjutsu seems inaccurate, as you can only ever, in your entire life, summon 1 type of animal.

So actually there's also Spider and Monkey types as well as the ones I mentioned above. But we don't know enough about them to be able to make code, as in both cases they only ever summoned 1. The Spider laid eggs which hatched all over Neji, and the Monkey could turn invisible, but that still didn't help the 3rd Hokage.

[Yamashita]

I would wager that the "blood" you are referring to is bloodline techniques, which are often varying types of nin- or gen-jutsus.